The regulation of surface synthesis in the oral pathogen Streptococcus mutans will be studied by a combination of physiological and genetic methods. We will examine the basis of penicillin resistance by transformation of derivatives of S. sanquis with plasmids containing DNA inserts obtained from a penicillin resistant S. mutans. We will also examine the structure and function of an approximately 7 kb DNA fragment that was inserted into an E. oli--streptococcal shuttle vector and that confers to S. sanguis grown on sucrose a colony morphology typical of S. mutans. The fragment also appears to cause the expression of S. mutans serotype c determinants in S. sanguis. We will also characterize several DNA fragmnts that can complement known defects in surface antigenicity of S. mutans by restoring normal surface structure. Lastly, we will initiate studies on the overall organization of the S. mutans genome and will examine the sructure of selected S. mutans promoters.